The present invention relates to the field of flat cables, particularly to the field of flat cables shielded against electromagnetic waves.
Flat cables consisting of a plurality of parallel wirings have been widely used.
Reference 101 in FIG. 13 represents a conventional flat cable comprising a plurality of wirings 112 longitudinally arranged in parallel on an elongate base film 111. Ten wirings 112 are shown in this figure.
A cover film 113 is applied on wirings 112 except for both ends of wirings 112, so that the part of each wiring 112 covered with cover film 113 forms a signal member 122 and the parts at both ends of the member not covered with cover film 113 form terminal members 121.
In order to electrically connect electric circuits using this flat cable 101, terminal member 121 at one end of flat cable 101 is connected to one electric circuit and terminal member 121 at the other end is connected to the other electric circuit.
Each wiring 112 consists of a copper foil having a thickness of several tens of micrometers, and the wiring 112, base film 111 and cover film 113 are flexible so that flat cable 101 can be folded to connect electric circuits.
Flat cable 101 as described above has been used in various devices in recent years, which raised the problem that flat cable 101 picks up noises.
If flat cable 101 were wholly covered with a metal foil, the metal foil could serve as an electromagnetic shield but involve a complex operation for grounding the metal foil.
The present invention was made to overcome the disadvantages of the prior art as described above with the purpose of providing a technique for easily and reliably accomplishing the grounding operation in a process for preparing a wiring board with a shield film.
In order to solve the above problems, the present invention provides a wiring board comprising a base film, a plurality of wiring members provided on the base film and bonded to the base film, a cover film provided on the wiring members, an opening formed in the cover film to expose the surface of a specific wiring member of the wiring members but not expose the surfaces of the other wiring members, and a shield film wrapped to cover both of the side of the base film and the side of the cover film, wherein the shield film is connected to the specific wiring member at the bottom of the opening.
A wiring board of the present invention is characterized in that the specific wiring member of the wiring members is wider than the other wiring members.
A wiring board of the present invention is characterized in that a terminal member is connected at each end of the each wiring member and at least a part of the terminal member is exposed from the cover film so that the shield film does not come into contact with the exposed part of the terminal member.
A wiring board of the present invention is characterized in that the shield film comprises a resin film, a conductor layer provided on the resin film and a conductive adhesive layer provided on the surface of the conductor layer and the conductive adhesive layer is in close contact with the surface of the cover film and the surface of the base film.
A process for manufacturing a wiring board of the present invention comprises patterning a metal layer on a base film in a predetermined shape to form a plurality of metal wirings, providing a cover film having an opening on the metal wirings in such a manner that the opening overlies a specific metal wiring of the metal wirings, and wrapping a shield film from the side of the base film to the side of the cover film.
A process for manufacturing a wiring board of the present invention comprises providing a plurality of wiring sets consisting of the metal wirings on a predetermined region of the base film, forming the opening in the number equal to or greater than the number of the wiring sets in the cover film in such a manner that at least one opening overlies the each wiring set, providing the cover film on the metal wirings and then cutting the base film and the cover film to separate the wiring sets.
According to the present invention as defined above, a specific wiring member and a shield film are electrically connected at the bottom of an opening in a cover film and the shield film is wrapped from the side of the cover film to the side of the base film, whereby the shield film can be placed at ground potential on not only the side of the cover film but also the side of the base film.
Each wiring member consists of a metal layer patterned in a predetermined pattern and a specific wiring member is patterned to be wider than the other wiring members. Therefore, the specific wiring member is exposed at the bottom of the opening even if the opening made in a large diameter is positioned, and the opening can be easily aligned with the specific wiring member.
The part of the terminal member exposed from the cover film connected to each end of each wiring member is electrically exposed without contact with the shield film, whereby the terminal member can be easily connected to a connector of another electronic circuit.
The shield film comprises a resin film, a conductor layer and a conductive adhesive layer stacked in the order mentioned and is wrapped in such a manner that the conductive adhesive layer is in close contact with the cover film and the base film, whereby the shield film can be bonded to the surfaces of the cover film and the base film without applying an adhesive on the surfaces of the cover film and the base film or the surface of the shield film.
In the state where the shield film is wrapped, the resin film is located on the outside of the wiring board and the resin film protects the conductor layer, whereby no short circuit occurs even if the wiring board of the present invention comes into contact with another electronic component.